Acetogenic microorganisms are known to be useful for the production of fuels (for example, ethanol or butanol) and other chemicals by fermentation of substrates including carbon monoxide, carbon dioxide, hydrogen and methanol, for example. Many of these microorganisms naturally produce at least two, if not more, products. However, where micoorganisms are being used to produce products, particularly on a commercial scale, it is not always desirable for the microorganisms to produce multiple products. For example, production of multiple products can come at the expense of production efficiency and yield of a product of particular value, as by-products can divert carbon away from the pathways involved in producing the main desired product. In addition, by-products may be toxic to the microorganism, the production of multiple products can make recovery and separation of desired products difficult and, it can be difficult to control fermentation conditions to favour production of one product over another. By-products may also be a potential source of contamination in a fermenter as they may be substrates for undesirable organisms.
In the case of ethanol production by microbial fermentation of substrates comprising carbon monoxide, 2,3-butanediol is typically produced as a by-product. This may reduce the ethanol production efficiency and yield, as well as cause other problems, as noted above.
It is an object of the invention to overcome one or more of the disadvantages of the prior art, or to at least to provide the public with a useful choice.